1. Field of the Invention
This invention relates to the field of hydrocarbon conversion processes. More particularly, this invention relates to hydrocracking partially refined petroleum products such as distillation residuals of coal, coal extracts and the like, to form more valuable products. Still further, this invention relates to a method for hydrocracking a hydrocarbonaceous material in an alkali metal hydroxide melt.
2. Description of the Prior Art
The steadily increasing demand for distillate petroleum products and a decreasing supply of crude oils provides incentive for processes which upgrade high boiling petroleum residuals, coal, coal extracts, and other such polynuclear hydrocarbonaceous stocks. Such hydrocarbonaceous stocks usually contain sulfur, oxygen and nitrogen as well as various organometallic compounds. A suggested conversion process for upgrading such hydrocarbonaceous stocks is hydrocracking.
Hydrocracking is a decomposition of hydrocarbons at high pressures and elevated temperatures, with the addition of hydrogen and usually in the presence of a catalyst such as zeolite with a platinum, tungsten oxide, cobalt-molybdenum oxide or a nickel component. These catalysts may be altered by promotion with another metal or by some pretreatment such as sulfiding. Under these conditions hydrogenation occurs simultaneously with cracking. Thus, the buildup of tar or coke on the catalyst surface is substantially minimized. A number of problems are involved in these processes, however, including catalyst deterioriation caused by the sulfur, ammonia or ash in the feedstock, presence of hydrogen sulfide in the products, and catalyst deactivation resulting from coke deposition on the catalyst surfaces.
It has been proposed that many of these disadvantages can be overcome by a hydrocracking process employing a molten salt as a catalyst. It has been suggested, for example, to use zinc chloride or a zinc chloride mixed with a zinc oxide acceptor. The use of such molten salt catalyst does obviate many problems of the prior art. The catalyst in the form of a liquid offers a number of advantages, including excellent heat transfer characteristics and continual renewal of fresh catalyst surfaces. In addition, contaminants such as catalyst poisons can be withdrawn with a bleed stream of the molten salt to allow uninterrupted operation. The use of zinc chloride is not without problems, however, since zinc chloride is highly corrosive at elevated temperatures. Further, the solubility of the heavy hydrocarbons in molten zinc chloride is high and makes separation of the organic and salt phases difficult. In U.S. Pat. Nos. 3,677,932 and 3,736,250 it is suggested that the solubility of the zinc halide for hydrocarbon may be substantially reduced by the addition thereto of certain alkali metal halides. These processes still are not altogether satisfactory in that separation of the hydrocarbon products from the salt is still difficult. Further, the regeneration of such mixed salts is a complex procedure requiring high-temperature treatment in a corrosive atmosphere.
In U.S. Pat. No. 3,745,109 there is disclosed a hydrocarbon conversion process. Hydrocarbons such as partially refined petroleum are contacted with a sulfide-containing alkali metal carbonate melt. In the presence of hydrogen and at the appropriate temperature and pressure conditions the partially refined petroleum is hydrocracked. This process, although obviating many of the problems of the prior art zinc chloride processes, still is not altogether satisfactory. More particularly, the yields obtainable are lower than is desirable. A commercially viable hydrocracking process should provide a conversion of at least of 75 to 80% of the feedstock. Further, at least about 60 wt.% of the product should be obtained as a normally liquid product substantially free of sulfur and metallic ash constituents such that it is suitable for use as a feed material to a conventional petroleum refinery.
U.S. Pat. No. 3,846,275 suggests a coal liquefaction process, which comprises contacting a solid carbonaceous material with a reducing gas, water, and a catalytic compound containing a sulfur component and an alkaline metal ion, or ammonia ion at liquefaction conditions to produce a mixture comprising an aqueous phase and a hydrocarbonaceous phase which are separated. The hydrocarbonaceous phase then is extracted with a hydrocarbonaceous solvent to provide an extract fraction and a solid residual fraction. The liquefaction product is recovered from the extract fraction.
A similar process is disclosed in U.S. Pat. No. 3,796,650. The suggested process comprises contacting coal with water, at least a portion of which is in a liquid phase, a reducing gas, and a compound selected from ammonia and carbonates and hydroxide of alkali metals, at liquefaction conditions including a temperature of 200.degree. to 370.degree. C to provide a hydrocarbonaceous product. It is a disadvantage of both the foregoing processes that the yield of liquid product and amount of feed material converted is less than desirable. In addition, such processes require an aqueous phase reaction. The high temperatures necessarily result in a requirement for excessively high pressures to maintain the aqueous phase.
Another such aqueous process is disclosed in U.S. Pat. No. 3,642,607, wherein a mixture of coal, a hydrogen donor oil, carbon monoxide, water, and an alkali metal hydroxide are heated to a temperature of about 400.degree. to 450.degree. C, and under a total pressure of at least about 4000 psig to obtain dissolution of the coal. However, this process suffers from the same disadvantages as the other aforementioned aqueous processes.
Thus, it is seen that each of the above noted conversion processes is in need of improvement.